First pass of the Nextflow Run course (#626)

Abridged version of Hello Nextflow focused on running rather than developing.

 - Run basic operations (Hello World level)
 - Run pipelines (channels for multiple inputs, multi-step example, modules, containers)
 - Configuration

Author: vdauwera

docs/nextflow_run/00_orientation.md

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+# Orientation
+
+This orientation assumes you have already opened the training environment by clicking on the "Open in GitHub Codespaces" button.
+If not, please do so now, ideally in a second browser window or tab so you can refer back to these instructions.
+
+[![Open in GitHub Codespaces](https://github.com/codespaces/badge.svg)](https://codespaces.new/nextflow-io/training?quickstart=1&ref=master)
+
+## GitHub Codespaces
+
+The GitHub Codespaces environment contains all the software, code and data necessary to work through this training course, so you don't need to install anything yourself.
+However, you do need a (free) GitHub account to log in, and you should take a few minutes to familiarize yourself with the interface.
+
+If you have not yet done so, please go through the [Environment Setup](../../envsetup/) mini-course before going any further.
+
+## Working directory
+
+Throughout this training course, we'll be working in the `nextflow-run/` directory.
+
+Change directory now by running this command in the terminal:
+
+```bash
+cd nextflow-run/
+```
+
+!!!tip
+
+    If for whatever reason you move out of this directory, you can always use the full path to return to it, assuming you're running this within the GitHub Codespaces training environment:
+
+    ```bash
+    cd /workspaces/training/nextflow-run
+    ```
+
+Now let's have a look at the contents of this directory.
+
+## Materials provided
+
+You can explore the contents of this directory by using the file explorer on the left-hand side of the training workspace.
+Alternatively, you can use the `tree` command.
+
+Throughout the course, we use the output of `tree` to represent directory structure and contents in a readable form, sometimes with minor modifications for clarity.
+
+Here we generate a table of contents to the second level down:
+
+```bash
+tree . -L 2
+```
+
+If you run this inside `nextflow-run`, you should see the following output:
+
+```console title="Directory contents"
+.
+├── 1-hello.nf
+├── 2a-inputs.nf
+├── 2b-multistep.nf
+├── 2c-modules.nf
+├── 2d-container.nf
+├── 3-main.nf
+├── modules
+│   ├── collectGreetings.nf
+│   ├── convertToUpper.nf
+│   ├── cowpy.nf
+│   └── sayHello.nf
+├── nextflow.config
+└── test-params.yaml
+
+1 directory, 12 files
+```
+
+**Here's a summary of what you should know to get started:**
+
+- **The `.nf` files** are workflow scripts that are numbered based on what part of the course they're used in.
+
+- **The file `nextflow.config`** is a configuration file that sets minimal environment properties.
+  You can ignore it for now.
+
+- **The file `greetings.csv`** contains input data we'll use in most of the course. It is described in Part 2, when we introduce it for the first time.
+
+- **The file `test-params.yaml`** is a file we'll use in Part 3. You can ignore it for now.
+
+**Now, to begin the course, click on the arrow in the bottom right corner of this page.**